Chapter 7 Earth and the Terrestrial Worlds

Transcription

1 Chapter 7 Earth and the Terrestrial Worlds

2 Earth s Interior Core: Highest density; nickel and iron Mantle: Moderate density; silicon, oxygen, etc. Crust: Lowest density; granite, basalt, etc.

3 Terrestrial Planet Interiors Applying what we have learned about Earth s interior to other planets tells us what their interiors are probably like.

4 Why do water and oil separate? 1. Water molecules repel oil molecules electrically. 2. Water is denser than oil, so oil floats on water. 3. Oil is more slippery than water, so it slides to the surface of the water. 4. Oil molecules are bigger than the spaces between water molecules.

5 Differentiation Gravity pulls high-density material to center Lower-density material rises to surface Material ends up separated by density

6 What is necessary for differentiation to occur in a planet? It must have metal and rock in it. 3. It must be a mix of materials of different density. 4. Material inside must be able to flow. 5. All of the above and 3.

7 Do rocks s-t-r-e-t-c-h? 1. No rock is rigid and cannot deform without breaking. 2. Yes but only if it is molten rock. 3. Yes rock under strain may slowly deform.

8 Heat Drives Geological Activity Convection: hot rock rises, cool rock falls. One convection cycle takes 100 million years on Earth.

9 Sources of Internal Heat 1. Gravitational potential energy of accreting planetesimals 2. Differentiation 3. Radioactivity

10 Heating of Interior over Time Accretion Radioactive decay

11 Cooling of Interior Convection Conduction Radiation

12 What cools off faster? 1. A grande-size cup of Starbucks coffee 2. A teaspoon of cappuccino in the same cup

13 What cools off faster? 1. A big terrestrial planet 2. A tiny terrestrial planet

14 Role of Size Smaller worlds cool off faster and harden earlier. Moon and Mercury are now geologically dead.

15 Surface Area to Volume Ratio Heat content depends on volume. Loss of heat through radiation depends on surface area. Time to cool depends on surface area divided by volume: surface area to volume ratio = 4"r2 4 3 "r3 = Larger objects have a smaller ratio and cool more slowly. 3 r

16 Planetary Magnetic Fields Moving charged particles create magnetic fields. A planet s interior can create magnetic fields if its core is electrically conducting, convecting, and rotating.

17 Earth s Magnetosphere Earth s magnetic fields protects us from charged particles from the Sun. ( Northern lights ).

18 If the planet core is cold, do you expect it to have magnetic fields? 1. Yes, refrigerator magnets are cold, and they have magnetic fields. 2. No, planetary magnetic fields are generated by moving charges around, and if the core is cold, nothing is moving.

19 How does Earth s atmosphere affect the planet? Which Molecules are Greenhouse Gases?

20 Effects of Atmosphere on Earth 1. Erosion 2. Radiation protection 3. Greenhouse effect 4. Makes the sky blue!

21 Radiation Protection

22 The Greenhouse Effect Which Molecules are Greenhouse Gases?

23 Greenhouse effect: Certain molecules let sunlight through but trap escaping infrared photons. (H 2 O, CO 2, CH 4 ) The Green House Effect

24 Why is the sky blue? 1. The sky reflects light from the oceans. 2. Oxygen atoms are blue. 3. Nitrogen atoms are blue. 4. Air molecules scatter blue light more than red light. 5. Air molecules absorb red light.

25 A Greenhouse Gas Any gas that absorbs infrared Greenhouse gas: molecules with two different types of elements (CO 2, H 2 O, CH 4 ) Not a greenhouse gas: molecules with one or two atoms of the same element (O 2, N 2 )

26 Why the sky is blue

27 Long-Term Climate Change Changes in Earth s axis tilt might lead to ice ages. Widespread ice tends to lower global temperatures by increasing Earth s reflectivity. CO 2 from outgassing will build up if oceans are frozen, ultimately raising global temperatures again.

28 How is human activity changing our planet?

29 Dangers of Human Activity Human-made CFCs in the atmosphere destroy ozone, reducing protection from UV radiation. Human activity is driving many other species to extinction. Human use of fossil fuels produces greenhouse gases that can cause global warming.

30 Global Warming Earth s average temperature has increased by 0.5 C in the past 50 years. The concentration of CO 2 is rising rapidly. An unchecked rise in greenhouse gases will eventually lead to global warming.

31 CO 2 Concentration Most of the CO 2 increase has happened in last 50 years!

32 Modeling of Climate Change Complex models of global warming suggest that the recent temperature increase is indeed consistent with human production of greenhouse gases.

33 What makes a planet habitable? Located at an optimal distance from the Sun for liquid water to exist

34 Where did Earth s (interior) heat come from? 1. Volcanoes 2. Impacts as Earth was accreting 3. Radioactivity 4. All of the above 5. 2 and 3

35 What is necessary for a differentiation to occur in a planet? 1. It must have metal and rock in it 2. It must be a mix of materials of different density 3. Material inside must be able to flow 4. All of the above 5. 2 and 3

36 What is the source of Earth s magnetic field? 1. Magnetic rocks 2. Magnetized iron in Earth s crust 3. Magnetized iron in Earth s core 4. Molten metal circulating inside of Earth, moving electrons like in a wire

37 What is the greenhouse effect? 1. Something bad that happens to the atmosphere 2. Something bad that happens to the atmosphere if we lose too much ozone 3. Something bad that is happening on Earth, not other planets 4. 1, 2, and 3 5. Visible light enters an atmosphere and heats a planet, then the planet emits infrared light that is trapped by the atmosphere

38 If there was no greenhouse effect, Earth: 1. Would be safer than it is today 2. There would be no human presence, since humans make the greenhouse effect 3. Earth s average temperature would be colder than freezing 4. We would be in danger from ultraviolet radiation

39 Why are smaller terrestrial bodies such as Mercury or the Moon geologically dead? 1. They don t have volcanoes 2. They cooled off faster than Earth did 3. They don t have erosion 4. They were hit by fewer meteorites 5. They are made of different materials than Earth